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UDP Protocol

UDP (User Datagram Protocol) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP). UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the Transmission Control Protocol, UDP uses the Internet Protocol to actually get a data unit (called a datagram) from one computer to another. Unlike TCP, however, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may prefer UDP to TCP. The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.
UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact.

UDP provides simple, low-level communication between processes on computers. Processes communicate by sending datagrams to a destination computer or port. A port is the location where you send data. IP handles the computer-to-computer delivery. Once the datagram reaches the destination computer, UDP moves the datagram to its destination port. If the destination port is not open, UDP discards the datagram. UDP shares all the delivery problems of IP.

Use UDP in applications where reliability is not critical. For example, an application might transmit informative data to a destination frequently enough that a few lost segments of data are not problematic.

Using UDP
Because UDP is not a connection-based protocol as TCP is, you do not need to establish a connection with a destination before you send or receive data. Instead, you specify the destination for the data when you send each datagram. Operating systems do not report transmission errors.

Use the UDP Open function to open a port. The number of simultaneously open UDP ports depends on the operating system. UDP Open returns a UDP Network Connection refnum, which is an opaque token used in all subsequent operations that pertain to that port.

Use the UDP Write function to send data to a destination and use the UDP Read function to read that data. Each write operation requires a destination address and port. Each read operation contains the source address and port. UDP preserves the datagram bytes that you specified for each command you send.

In theory, you can send datagrams of any size; however, you would not typically use UDP to send large datagrams because it is not as reliable as TCP.

When you finish all communications on a port, use the UDP Close function to free system resources.

the big deal about udp is that its send and forget, unlike its more popular counterpart tcp which does all this handshaking and error checking ( which is great for downloading files and pictures ). if you are sending live audio or video streams error checking is not really a good idea.

lol u can always go to www.firewall.cx its a cool networking site... teaches u the ins and outs of networking and whats new.. btw.. that site is best viewed in MS IE.. coz the menue doest work on Opera..